1. Field of the Invention
The present invention relates generally to the field of bicycles and spoked wheels and more particularly to an improved spoked wheel suited for bicycles, wheelchairs, and motorcycles.
2. Background Art
A number of wheel designs have been made commercially available. The art of tensioned spoked wheels is one which dates back more than 100 years. Modern tensioned spoked bicycle wheels typically have between about 12 and 48 spokes. Generally, wheels with fewer spokes weigh less, but not always. At some point, as fewer spokes are used, the rims must become stronger because longer spans are unsupported, and thus the rim becomes heavier. The lightest possible rim results from a balance between the spoke number and design, the hub design, and the rim design.
Spoked wheels typically have a hub with two annular flanges, spokes, nipples, and a toroidal rim with a circumferential surface. The spokes attach at one end to the hub's annular flanges and at the other end to the circumferential rim surface via nipples. Some spokes have a “J” shape for hook attachment to the hub flange, and other spokes are essentially straight, with a head at one end and a thread at the other. In all cases, the spokes are substantially straight with the possible exception of the ends.
For bicycle front wheels that use rim brakes, the spokes can be radially laced, that is the spokes connect to the hub flanges in a path that would pass through the centerline of the hub. For bicycle or motorcycle front wheels with disc or drum brakes, at least some of the spokes attach tangentially to the hub flanges in order to better transfer the braking forces from the hub to the rim. Rear wheels that use rim brakes require at least some tangential spokes in order to transfer the torque of the rider or engine to the rim. Rear wheels that use disc or drum brakes also require tangential spokes. In the case of bicycles, the braking torque is higher than the drive torque of a person's legs, so the tangential spokes are even more important.
Traditionally, tensioned spokes from one hub flange alternately attach to the rim with the other hub flange, and at even spacing. Some newer tension spoked wheels have “paired spokes” wherein the spokes from one hub flange attach to the rim in proximity to spokes from the opposed hub flange. U.S. Pat. No. 5,938,293 (Dietrich) discloses a bicycle wheel with paired spokes attached closely together at the rim. Similarly, U.S. Pat. No. 6,679,561 (Addink et al.) discloses a bicycle wheel with paired spokes attached in proximity to the rim.
The advantage of traditional tensioned spoked wheels compared to paired spoke wheels is that for a given number of spokes, the unsupported spans of the rim are about twice as long for a paired spoke wheel. For example, for a 24 spoke wheel, the spokes will connect to 24 points evenly along a traditional spoked wheel rim, whereas for a paired spoke wheel, 24 spokes would attach to only 12 close regions along a pair spoked wheel rim, leaving longer unsupported sections of the rim. Note that even with paired spokes, the spokes always have some distance between their connecting points on the rim. The advantage of the paired spoke wheel is that the rim sees far lower loads that cause side wobble. So traditional spoked wheels induce lower hop forces and higher side wobble forces compared to pair spoked wheels.
U.S. Pat. No. 5,938,293, Dietrich discloses a paired spoke wheel wherein the spokes are paired along the same radial position, and apart from each other transversely. This type of pairing produces a twisting load on the rims because of the distance between the spoke connections. The spokes cannot be placed any closer together because of nipple access and wall material availability in the rim.
The spokes of prior art wheels attach to the circumferential rim surface via nipples or, in the case of some straight pull spokes, a flanged spoke end. There is a high concentration load at each point of spoke attachment. Rims are often made by an extrusion process, thus having a consistent rim floor thickness along this attachment surface. In order to make this rim attachment wall strong enough for the spokes, the wall is inherently stronger than necessary in the areas away from the spoke attachment points. In some wheels, spacers or eyelets are used to reinforce the attachment points, but the loads are still relatively concentrated. U.S. Pat. No. 6,402,256 (Mercat) discloses a traditional bicycle rim, wherein the otherwise consistent inner rim floor has been partially machined away between the points of spoke attachment. Note that this is a circumferentially oriented wall and not a radially oriented wall.
Spoked wheels that attach to the hub via the nipples are difficult to adjust because access to the nipples is limited. Oftentimes, the spoke wrench can only turn the nipples 45 degrees of a turn before the wrench needs to be removed and placed on the nipple again. This is an extremely cumbersome way to adjust the spoke tension. Paired spoke wheels with nipples attached at the rim can have this same problem of cumbersome spoke tension adjustment because the close proximity of the spoke connections interferes with rotating the spoke wrench a full turn during adjustment. Regardless of the wheel type, all spoke nipples are relatively short compared to the length of the spoke.
Traditionally, spoked wheels require inner tubes because otherwise, holes in the rim for the spokes would cause air leakage. Typically, the rim has two flanges for holding the bead of the tire, a circumferential wall to hold the flanges, and another circumferential wall forming the inner rim floor for spoke attachment. Typically, the spoke holes are machined through both circumferential walls in order to be able to insert the nipples. Some newer tubeless spoked wheel designs for bicycles have holes in the rim that are machined only through the rim floor for spoke attachment so that air cannot leak out of a tubeless tire. This also strengthens the rim, although manufacturing the rim is more difficult.
If a spoke breaks, the wheel will suddenly become out of true because of the imbalance in tensions. If a spoke breaks during a ride and is not replaced immediately, the wheel may need to be trued before riding continues in order to prevent the rim from rubbing on the brakes or frame. If the rider adjusts the spoke tensions to compensate for the broken spoke, then the wheel needs to be trued again after the spoke is replaced. Therefore, some riders carry a spare spoke to replace a broken spoke while in the middle of a ride. Replacing the spoke on the front wheel or the non-drive side of the rear wheel is oftentimes faster than not replacing the spoke and then adjusting the other spokes to compensate for the broken spoke. Additionally, this relieves stress on the wheel by balancing the tensile loads according to the original design. However, it is typically difficult or impossible to replace a drive side rear spoke with current hub designs without using special tools.
Prior art hubs are usually machined from bar stock of material with an outer diameter about the same size as the maximum flange or rib diameter of the hub. A tremendous amount of aluminum is wasted during this process.
Prior art wheels have inboard and outboard spokes. For wheels with ribs for spoke attachment wherein there are two spokes per rib, the mounting points are next to one another and equidistant from the centerline of the hub. This causes the inboard spokes to be more substantially inboard from the outboard spokes, weakening the wheel.